Ecological determinants and sensory mechanisms in habitat selection of crustacean postlarvae

Animals use sensory stimuli to assess and select habitats, mates, and food as well as to communicate with other individuals. One of the great mysteries of crustacean ecology, is how postlarvae locate the relatively rare patches of coral reef habitat on which they settle. The present study aimed to estimate, by experiments in aquaria and biochemical analysis, the sensory modalities of crustacean postlarvae for senses used in searching for their species' settlement habitat. The study was carried out on 9 crustacean species (Calappa calappa, Pachygrapsus planifrons, Xanthidae sp., Lysiosquillina maculata, L. sulcata, Raoulserenea sp. Stenopus hispidus, Palaemonidae sp., and Panulirus penicillatus). For each species, a cohort of 30 postlarvae was captured on the same night on the reef crest of Rangiroa Atoll (French Polynesia). Among the 9 crustacean species studied, 6 made active habitat choices among the 4 habitats tested (live coral, dead coral, macroalgae, and sand) at the postlarval stage, but the presence or absence of conspecifics on the habitat did not influence their selective choice. Sensory experiments found that 4 species differentiated between their preferred habitat versus another habitat and 2 species differentiated between conspecifics and heterospecifics, using visual and/or olfactory cues. Lastly, the high performance liquid chromatography experiments showed that the 4 habitats and conspecifics (except L. maculata and S. hispidus) tested have different and unique chemical odors. Overall, our study is the first to highlight the sensory modalities for a broad range of crustacean species to detect and move toward settlement habitats and/or conspecifics.